DESCRIPTION (Taken from the applicant's abstract): Dr. Susan Bartlett has a clinical background in weight loss and exercise. Her commitment to clinical research is said to be demonstrated by her investment of many years with the Obesity Research Group at the University of Pennsylvania, return to graduate school obtain Ph.D. training in research methodology and interventions as a clinical psychologist, as well as completion of a fellowship in Weight Management at the Johns Hopkins School of Medicine. Knee osteoarthritis (OA) is a major public health challenge affecting millions of people in the US. Obesity is a primary target for intervention since it accounts for up to 30% of knee OA, exacerbates symptoms and is associated with bi-lateral involvement and more rapid progression of the disease. While the American College of Rheumatology Practice Guidelines recommends modest weight loss as symptomatic therapy, to date no published clinical trials have investigated the impact of weight loss on knee OA. Physical activity has also been associated with pain reduction and increased mobility in individuals with knee OA and should included in treatment (ACR Practice Guidelines). Exercise may be especially helpful for overweight persons with knee OA as it is a potent predictor of maintenance of weight loss. Though adherence to traditional exercise programs has been poor, lifestyle in which exercise is accumulated throughout the day appears to be a promising new approach to physical activity. Lifestyle physical activity has been associated with both health and weight loss benefits. Lifestyle exercise may also enhance exercise adherence by increasing options to be active and reducing time barriers. Episodes of physical activity may be preferable to continuous exercise in reducing pain and avoiding injury. The primary objective of this proposal is to evaluate the impact of weight loss and lifestyle exercise on knee osteoarthritis. To accomplish this, 156 overweight persons with symptomatic knee OA will be randomized to receive a 16-week program of: 1 ) a weight loss + lifestyle physical activity; or 2) health education (control). The primary outcome measure will be knee pain. Secondary measures include physical disability, quality of life, performance measures and long-term adherence to behavior change. This study will provide data on integrating behavioral changes into the treatment of knee OA.